MPCB (motor protection circuit breaker) - Earth Fault

[doremami]

Hi dears,
Can an earth fault cause an MPCB to burn? We have heaters in the turbogenerator where an earth fault has occurred. But the MPCB in the feeder of these heaters has burned. I think when an earth fault occurs in the heater, a high current flows which should lead to the circuit being cut off. Not that the MPCB itself is faulty. Is that correct?

 

[FacEngrPE]

Seems like applying a MPCB to a heater circuit would be a misapplication, in the NEC world the correct device would be a Circuit breaker with ground fault (30mA?) trip.

Please provide a snapshot of the device label.
Do you have an estimate of the available fault current?

As often stated by others here more information provides better answers.

 

[waross]

We have heaters in the turbogenerator where an earth fault has occurred.
Was the fault in the turbogenerator circuit or in the heater circuit?
A fault starting in the turbogenerator that crosses over to the heater circuit may easily provide a voltage and current beyond the capability of the MPCB.
And a motor circuit breaker may be a simple instantaneous trip, or it may be a full featured motor starter, including ground fault protection.
In the case of an instantaneous only device, the circuit impedance may limit the fault current to less than the trip setting.

 

[LionelHutz]

Pretty sure the question is about a MCP.

MCP - instantaneous trip only.
MCCB - thermal-magnetic or overload and instantaneous trip.

A MCP is the wrong protection device for a heater circuit. A MCP should only be used for protecting a motor circuit with an overload.

 

[jraef]

By virtue of the use of “earth fault” instead of ground fault, I hazard a guess that the OP is not in North America, so rules and terminology are different.

An MPCB is a thermal-mag circuit breaker with adjustable thermal trips. We use them here, but many people are as yet unfamiliar with them. Think “manual motor starter” in the form of an MCCB. In countries outside of NA, they can use those in ways we cannot.

I’m in agreement with what waross has hypothesized; a possible crossover fault of the heater into the generator windings and an earth fault of a magnitude far in excess of what the MPCB was capable of handling.

But alternatively, an internal ARCING fault in just the heater itself can be of such high resistance that the current remains BELOW the trip setting on the breaker for an extended time. That technically shouldn’t cause damage to the BREAKER, but might have exacerbated an issue with a loose connection that went unobserved under normal operating conditions.

 

[doremami]

We have heaters in the turbogenerator where an earth fault has occurred.
Was the fault in the turbogenerator circuit or in the heater circuit?
A fault starting in the turbogenerator that crosses over to the heater circuit may easily provide a voltage and current beyond the capability of the MPCB.
And a motor circuit breaker may be a simple instantaneous trip, or it may be a full featured motor starter, including ground fault protection.
In the case of an instantaneous only device, the circuit impedance may limit the fault current to less than the trip setting.

Was the fault in the heater circuit.